Today (Thursday), a National Crime Agency spokesman said: “Hertfordshire police officers, working as part of an NCA-led investigation, arrested a 19-year-old man in Watford today on suspicion of blackmail and making malicious communications relating to the hoax bomb threat that closed hundreds of UK schools this week.

“We understand parents’ and teachers’ concerns but stress there was no credible threat to the emails schools received. However we are taking the communications extremely seriously.

“As this is now a live investigation we are unable to comment further.”